1. Field of the Invention
The present invention relates to an anti-reflection film to prevent external light from reflecting on a window or a surface of display devices etc. Specifically, the present invention relates to an anti-reflection film applied on a surface of liquid crystal displays (LCDs) or transmission type LCDs.
2. Description of the Related Art
In general, displays are used under external light whether they are used indoors or outdoors. The external light incident to a display surface is reflected on the surface so that a displayed image is interfered with by the reflected image and the quality of display decreases. Hence, it is necessary to provide a display surface with an anti-reflection function, and further, improvements of the anti-reflection function along with introductions of other extra useful functions are being demanded.
The anti-reflection function is generally obtained by forming an anti-reflection layer of a multilayer repeating high and low refractive index sub-layers made of a transparent material such as metal oxides etc. on a transparent substrate. The anti-reflection layer of such a multilayer can be formed by a dry coating method such as chemical vapor deposition (CVD) and physical vapor deposition (PVD). While having an advantage of being able to precisely control layer thicknesses of the high and low refractive index sub-layers, dry coating methods have a disadvantage of low productivity for mass production due to a deposition process under vacuum. Hence, wet coating methods, in which a coating liquid for forming an anti-reflection layer is used, are attracting attention as a forming method of the anti-reflection layer since they are, in contrast, applicable to a large size production, a continuous production and a low cost production of the anti-reflection layer.
In addition, in the case where the anti-reflection film is formed on a transparent film substrate, a production method in which the anti-reflection layer is formed on a hard coat layer made of a polyfunctional acrylic polymer preliminarily formed on the substrate is generally employed for the purpose of providing hardness to the relatively soft surface. While having a high level of surface hardness, gloss, transparency and abrasion resistance, the hard coat layer also has a strong insulation quality which easily results in charging. Hence, this production method has a problem of collecting dust and the occurrence of errors in a display production caused by charging due to a strong insulation quality
In order to provide the anti-reflection film with antistatic properties, a method of introducing a conducting agent and a method of arranging an antistatic layer between the hard coat layer and the anti-reflection layer have been disclosed.    <Patent document 1> JP-A-2005-202389    <Patent document 2> JP-A-2005-199707    <Patent document 3> JP-A-2006-016447    <Patent document 4> JP-A-H11-092750    <Patent document 5> JP-A-2004-004149    <Patent document 6> JP-A-2005-173216    <Patent document 7> JP-A-2005-297271    <Patent document 8> JP-A-2006-154758
In the method of introducing a conducting agent, there are problems of increasing material cost and hardness decrease of the hard coat layer etc. since a tremendous amount of conducting agent is required to obtain sufficient conductivity. Whereas in the method of arranging an antistatic layer, there are problems of color generation and unevenness due to the antistatic layer which is newly arranged between layers and generally has a high refractive index. Especially in the case where the antistatic layer and the anti-reflection (low refractive index) layer are formed by a wet coating method, there is a problem that in-plane thickness unevenness of the antistatic layer and the anti-reflection (low refractive index) layer tends to appear as a color unevenness of the resultant anti-reflection film.
In addition, in an anti-reflection film which has a hard coat layer, an antistatic layer and a low refractive index layer (anti-reflection layer) in the order of this description from the transparent substrate side, a polarizing layer and a second transparent substrate is arranged on the opposite side of a (first) transparent substrate from the side on which the anti-reflection layer is formed so that a polarizing plate which is applicable to a transmission type LCD is obtained. In the case where the polarizing plate employs iodine added elongated polyvinyl alcohol as a polarizing layer, there is a problem when it is applied on a transmission type LCD, that blue light leakage occurs during a black display state.